Vacuum brake boosters are well established in automotive engineering and widely used, in particular, in a passenger cars and light-duty commercial vehicles. When the brake pedal is actuated, such brake boosters generate an auxiliary force that boosts an actuating force exerted upon the brake cylinder by the brake pedal. This auxiliary force is generated by a pressure differential between two chambers in the brake booster, which are separated from one another by a movable diaphragm. During such a pedal actuation, atmospheric pressure, i.e. an ambient pressure of the surrounding air, is adjusted in the first chamber by a valve control. A vacuum is generated in the second chamber or so-called vacuum chamber.
The intake section of an internal combustion engine, in which a vacuum is generated, for example by an air volume flow while a throttle valve is closed, conventionally serves as a vacuum source for the vacuum in the vacuum chamber. To this end, the intake section and the vacuum chamber are connected to one another by a vacuum line and corresponding check valves.
In modern engines such as diesel engines or hybrid drive systems, the air volume flow in the intake section of the internal combustion engine may be either insufficient or not permanently available as a vacuum source depending on the operating state of the drive system. As a result, it has become common practice to provide an alternative or supplementary vacuum source for brake boosters in an increasing number of vehicles.
An alternative or supplementary vacuum source may be realized in the form of a vacuum system with a demand-driven vacuum pump having an electric vacuum pump. In addition to the demand-driven vacuum pump, such a vacuum system includes at least one vacuum line, one check valve and, if applicable, an exhaust air line. The exhaust air line may be realized in the form of an exhaust air hose that is installed in the engine compartment of a motor vehicle. The exhaust air line is connected to an exhaust port of the demand-driven vacuum pump with its first end. Its second end is routed to a desired location in the engine compartment.
The vacuum line and the check valve enable the demand-driven vacuum pump to convey an air volume from the vacuum chamber into the engine compartment and therefore into the external surroundings of the vacuum system through the second end of the exhaust air line such that a vacuum relative to the external surroundings, i.e. the atmosphere, is generated in the vacuum chamber.
The demand-driven vacuum pump or an electric vacuum pump can be activated and/or deactivated as needed by a pressure sensor or a pressure switch that monitors the vacuum in the vacuum chamber. When the demand-driven vacuum pump is deactivated, the vacuum in the vacuum chamber is initially maintained by the check valve until the vacuum is consumed, for example, as a result of corresponding brake boosting processes.
At the deactivation moment of the demand-driven vacuum pump, the vacuum prevailing at the check valve is essentially identical to the vacuum in the vacuum chamber. The ambient or atmospheric pressure simultaneously prevails at the second end of the exhaust air line. After the air volume flow conveyed by the demand-driven vacuum pump has been interrupted, the pressure gradient between the check valve and the second end of the exhaust air line causes the vacuum system to be ventilated with ambient air from the second end of the exhaust air line up to the check valve via the demand-driven vacuum pump. In other words, the air required for ventilating the vacuum system is taken in from the engine compartment of the respective motor vehicle through the second end of the exhaust air line.
Investigations have shown that splash water, which enters the engine compartment of a motor vehicle while it is driven in heavy rain, through water or under similar operating conditions, can be taken in by the vacuum system during such a ventilation process. These investigations have furthermore shown that splash water taken in through the second end of the exhaust air line can damage the demand-driven vacuum pump. The same problem also arises if the vacuum system does not include an exhaust air line such that splash water would in this configuration be directly taken in by the exhaust port of the demand-driven vacuum pump.